Diaphragm and composition of matter for forming the same



Patented May 30, 1933 UNITED STATES PATENT OFFICE GLEN. HARVEY BURGMAN, OF CHICAGO, ILLINOIS, ASSIGNOR TO G. T. LIEBICH COMPANY, OF CHICAGO, ILLINOIS DIAPHRAGM AND COMPOSITION OF FOR FORMING THE SAME No Drawing.

My invention relates to acoustic diaphragms and particularly to a composition of matter adapted for use in building or forming the same.

i It is a known practice to construct such diaphragms by suitably shaping a section of open mesh fabric, then filling the fabric to provide a degree of rigidity, then treating the surfaces with a pyroxylin lacquer containing metal salts or metallic solid matter in finely divided form, the composition being thinned with a volatile substance such as amyl acetate. The metal powder performs a very useful function in serving to prevent 5 the formation of a multitude of microscopic openings through the diaphragm. Such openings interfere seriously with efiiciency and tone quality in that they permit the passage of air through the vibratory element. This expedient, that is, the use of a finely divided metal such as powdered aluminum, is an essential where a coating material is used that hardens by evaporation.

As the volatile matter is dissipated the solids become hard and this results in a surface containing a large number of voids; when the metal powder is used in sufficient quantity and is thoroughly disseminated, the metal particles fill all such holes and render 0 the diaphragm air impervious.

However, a diaphragm containing a suflicient quantity of metallic solids to fill the voids and prevent the formation of pin holes results in sound reproduction with a metal )5 ring; in other words, a brassy tone is distinguished from the true tone, and this is to be avoided.

An object of my invention is to provide a diaphragm in which the coating material is hardened by polymerization and oxidation in order to avoid the formation of pin holes in a metal-free film. This result is secured by the utilization of gums or resins and drying oils and without any metallic solids. F The solvent which I prefer to use as a thinner may be volatile and be dispersed by evaporation, but the remaining film is still in a semi-fluid condition after the solvent has disappeared. This film will tend to 5 spread rather than contract and will fill up Application filed August 4,1931. Serial No. 555,137.

A diaphragm can be constructed solely of the described materials but for greater resistance to breakage I prefer to incorporate in the body of material a reinforcement of fibrous material such as fabric or an open fibre paper.

In the process of forming such a diaphragm, I provide a section of fabric or paper, first filling it with a'starch or sizing solution, then shaping and drying it and then spraying or dipping the so formed element with the composition of matter of my invention. This may preferably consist of a, compound of approximately non-volatile ingredients and 50% of a volatile solvent. The solvent may consist of approximately equal parts of light and heavy naphtha. The non-volatile matter may properly consist of equal parts of Ester gum and resin, and drying oils, consisting ofa mixture of linseed oil and china wood oil in a proportion of 1 to 4. Care should be taken to avoid the inclusion of any metallic dryer or any metallic solids. I

After the diaphragm base has been fully covered with the composition, it is allowed to dry to dissipate the volatile matter, and is then baked to set the drying oil. The resulting diaphragm is free from microscopic holes, is water repellant and very light in weight and sensitive to vibrations. Tests of such diaphragms have indicated remarkably high eificienoy and tone quality.

The gummy solid matter may consist of any of the gums commonly used in the varnish industry such as gum Damar, Ester gum, resin, bakelite, etc. The drying oil may consist of linseed oil, china wood oil or a mixture of these or similar drying oils. While we have found that satisfactory results are secured by using four parts of china wood oil to one part of linseed oil, this proportion may be varied somewhat. Also that the roportion of volatile matter may be varie in order to adapt the compound to different forms of application; at any rate, it should be understood that my invention contemplates the elimination of all metallic matter and of the use of a surface coating that hardens other than by evaporation.

I emshmizethe intthatacoa i a sho dbeused *attendstosprea in ing in order to insure an air empervious without the use of metal owder or other solids that tend to im air e tone reproducing quality of the vibratory element.

Obviously the composition is capable of i variation in several particulars, and I do 5 not wish to be limited except as indicated in the appended claims.

I am:

1. An acoustic diaphra comprisi a fibrous reinforcement and i body of aiiimpervious water repellant material consisting of gums,- resins and drying oils, in which the pro rtion of the gums and resins to the oils ass ut'equal.

.2. An acoustic diaphragmcomprising a 2 fibrous reinforcement and a body of air-impervious, water repellant material consisting of gums and resins, and oils in the proportion of four parts of a wood oil to one part of linseed oil.

80 8. A composition of matter for use in acoustic diaphra consisting of a non-metallic gummy so 'd, a non-volatile drying oil and a volatile thinner, the roportion of volatile matter to the who e compoundbeing not -.;t r than 50%, the combemg from metal salts or 4.A composition of matter for use in making acoustic diaphra consisting of a 40 nonsmetallic gummy soli and a non-volatile oil in substantially equal arts. 5. composition: matter or use in making acoustic consisting of W and 1a non-volatile drying 5 oil a Vela-mixer.

-In any whereof I have afixed my signature. 7 I

, GLEN HARVEY BURGMAN. 

